Gold and gold alloy electroplating



United States Patent C) 3 373,094 GOLD AND GOLD ALLOY ELECTROPLATING Donald Gardner Foulke, Plainfield, NJ., assignor to Sel- Rex Corporation, Nutley, N.J., a corporation of New Jersey No Drawing. Continuation-impart of application Ser. No. 392,286, Aug. 26, 1964. This application Oct. 18, 1965, Ser. No. 497,454

15 Claims. (Cl. 204-43) ABSTRACT OF THE DISCLQSURE Bright electroplated gold and gold alloys are obtained from an aqueous acid electroplating bath which contains as a brightening agent a proportion of piperazine or alkyl substituted piperazine.

This application in a continuation-in-part of my US. application Ser. No. 392,286 filed Aug. 26, 1964, now abandoned.

This invention has to do with the electrodeposition of gold and more specifically with the electrodeposition of bright gold.

Bright gold deposits can be obtained from gold electrolytes containing alkali metal gold cyanide at a pH of about 3.0 to about 5.0 by adding base metal compounds such as nickel citrate, cobalt sulfate, etc., to the bath (see U.S. 2,905,601). One theory explains that such baths produce bright gold because they provide the base metal in the cathode film in a condition to codeposit with the gold. There may be conducting salts and buffering agents present, but the brightening action is attributed to the codeposition of gold and a suitable base metal. There are conditions, however, when the presence of metals other than gold in the deposit is undesirable. Sometimes the plating specification calls for 24 karat gold, in other cases the base metal present may be deleterious to a solidstate device to be gold plated.

Among the objects of the invention is to provide a process and electroplating bath for electroplating bright 24 karat gold without the codeposition of other metals with the gold.

This invention is based on the discovery that excellent bright gold deposits can be obtained by adding small amounts of piperazine or piperazine substitution compounds to acid electrolytes containing alkali metal gold cyanide even in the absence of codepositing metals.

It is common practice to add organic brightening agents to baths designed to electrodeposit base metals such as nickel and copper. Such addition agents have been used less frequently in silver and gold plating solutions and almost exclusively in alkaline baths, most of which contain considerable free alkali cyanide in addition to the alkali metal gold cyanide. The compounds disclosed in this invention, however, serve as a specific brightener in gold plating baths which are acid in nature, but when the pH of such vbaths rises much above 6, deposits plated out in the bath darken and lose brightness. Preferably the pH of the bath is also maintained above 3. The acid baths containing the piperazine compound give bright deposits from room temperature to about 60 C. or more.

At times acid gold baths formulated to give bright deposits by the addition of copper or nickel will have a limited bright range. Piperazine and its substitution compounds, when added to such baths produce an improved bright range with respect to current density. In addition other base metals, added as salts or chelates so as to be present in the cathode film in the condition necessary to co-deposit with the gold may be substituted for the copper or nickel to provide the bright deposits desired.

r 3,373,094 Patented Mar. 12, 1968 The specific brightening agents are piperazine and the substituted piperazines and the amount added to the bath is not critical, 0.5 to 50 g./l. having been found effective. This will become apparent in the examples set forth below.

The term substituted piperazine will be understood to include those fairly simple substitution compounds obtained by substituting alkyl groups for one or more of the hydrogens of the piperazine ring so that the compound does not lose its essential piperazine characteristics.

Conducting salts which are preferably alkali metal or ammonium salts may be added to said baths as such or may be formed in the bath by the addition of the corresponding hydroxide or carbonate, etc., to react with a portion of the acid of said baths. Such salts also provide efiective buiiering for the solution, especially when the acids employed are weak acids.

Examples The conditions under which bright deposits may be obtained by means of this addition agent are so legion that the practice of this invention can best be shown in table form. Table I indicates the acid used, which in each case was neutralized to the pH listed with KOH or NaOH to provide the conducting and buffer salts (since the acids employed in these examples are weak acids).

TABLE I.BATH COMPOSITIONS ExampleNo 1 2 3 4 5 6 7 8 9 Constituent:

KAu (ON); 6 Piperazine Dimethyl Pipera inn Citric acid Tartaric acid 2 Acetic acid- Maleic acid. Phosphoric acid- Polyphosphoric acid.. 50 100 pH 3.0 4.5 4.0 5.8 4.5 3.5 4.5 4.5

1 Amounts given are in 5.11. 2 NaAu(CN)z used for this bath and NaOH for neutralization.

When citric acid is added as the acid preferably 5-150 g./I. is employed.

Bright panels were obtained in all cases. The standard practice being to plate 10 x 2.5 cm. brass panels between two platinum cathodes in a liter beaker. Current densities from 0.1 to 5 amp./dm. were used, depending upon the temperature selected and the degree of agitation employed.

The following examples illustrate the action of the piperazine compounds on baths containing base metals.

Example 10 A bath containing potassium gold cyanide, 12 g./l.; copper ethylenediamine tetraacetate, 4 g./l.; antimony tartrate, 3 g./l.; potassium dihydrogen phosphate, 50 g./l.; and ethylenediamine tetraacetic acid, 20 g./l.; adjusted to a pH of 5.0, yielded deposits with a slight haze at 15 a.s.f. Upon the addition of dimethyl piperazine the deposits were fully bright.

Example 11 3 appended claims shall not be limited to any specific feature or details thereof.

I claim: a

1. An electroplating bath for producing bright gold deposits comprising an aqueous solution of alkali metal gold cyanide and as a brightening agent a compound selected from the group consisting of piperazine and alkyl substituted piperazine in an amount sufficient to produce a bright gold deposit, said bath having a pH below about 6.0.

2. An electroplating bath according to claim 1 in which the brightening agent is piperazine.

3. An electroplating bathaccording to claim 1 in which the brightening agent is dimethyl piperazine.

4. An electroplating bath according to claim 1 comprising in addition a suflicient amount of conducting salts to substantially lower the voltage required for deposition of the gold.

5. An electroplating bath according to claim 4 in which at least one conducting salt is a buffer and is present in an amount suficient to maintain a stable pH.

6. An electroplating bath according to claim 1 containing in addition base metal compounds of such a nature that at least one base metal is present in the cathode film in the condition necessary to co-deposit with the gold.

7. An electroplating bath for producing bright gold deposits comprising an aqueous solution of an alkali metal gold cyanide, at least one water soluble compound selected from the class consisting of alkali metal and ammonium salts of organic and inorganic acids to provide a pH below about 6 and as a brightening agent a compound selected from the group consistinng of piperazine and alkyl substituted piperazine in an amount suflicient to produce a bright gold deposit.

8. An electroplating bath as claimed in claim 7 wherein said brightening agent is piperazine.

9. An electroplating bath as claimed in claim 7 wherein said brightening agent is dimethyl piperazine.

10. An electroplating bath as claimed in claim 7 wherein said bath contains base metal ions selected from the group consisting of copper, nickel and mixtures thereof.

11. An electroplating bath according to claim 7 wherein the water-soluble compounds are the alkali metal and ammonium salts selected from the class of acids consisting of weak, stable, organic and inorganic acids.

12. An electroplating bath according to claim 7 in which the butler is partially neutralized citric acid in the amount of 5-150 g./l.

13. A method of electrodepositing bright gold which comprises electrolyzing an aqueous solution consisting essentially of a soluble alkali metal gold cyanide and piperazine in the amount of 0.5 to 5.0 grams per liter, said bath having a pH of about 3.0 to 6.0.

14. A method of electrodepositing bright gold which comprises electrolyzing at a current density of 0.1 to 5 I amp./dm. an aqueous solution comprising soluble alkali metal gold cyanide and as a brightening agent a compound selected from the group consisting of piperazine and alkyl substituted piperazine in a amount sutficient to produce a bright gold deposit, said bath having a pH of about 3 to 6. i

15. A method as claimed in claim 14 wherein said added brightening agent is dimethyl piperazine.

References Cited UNITED STATES PATENTS Ostrow et al 20443 HOWARD S. WILLIAMS, Primary Examiner.

JOHN H. MACK, Examiner.

G. KAPLAN, Assistant Examiner. 

